During the past year, the laboratory has succeeded in purifying to homogeneity small amounts (10 to 50 micrograms) of the plasminogen activator (PA) from Rous sarcoma virus-transformed chicken embryo fibroblasts (RSVCEF). A synergistic enhancement of PA production brought on by treatment of RSVCEF with the tumor promoter phorbol myristic acetate (PMA) has provided an enriched source of PA (serum-free culture fluid from the PMA-treated RSVCEF cultures). The purification steps include affinity chromatography, ion exchange, and gel filtration chromatography and polyacrylamide gel electrophoresis. The biochemical characterization and the use of the enzyme in add-back experiments await the production of larger quantities of PA. In order to accomplish this, antibody against the enzyme is now being produced so that a monospecific antibody linked to Sepharose can be employed for large-scale purification. In addition, the antibody will serve as a probe to examine the role of PA in malignant transformation. The mechanism of how a tumor promoter (PMA) can synergistically elevate a transformation-specific enzyme is also under investigation. The RSVCEF system is ideal since the production of PA is closely correlated with malignant transformation, the cells are extremely sensitive to PMA, and an antibody to the purified enzyme will soon be available. (A)